GWEN IFILL: For those stations not taking a pledge break, we have a report on the resurgence of whooping cough in California. Tonight's story comes from reporter Joanne Faryon of KPBS in San Diego.
JOANNE FARYON: Matthew Jacob Bryce was born Oct. 11, 2010, a healthy baby, a third boy for Cindy and Marlon Bryce. Matthew started showing signs of a cold when he was just two weeks old. The Bryce family knew something was wrong.
MARLON BRYCE: It just seems like this cold was just like -- it was just affecting his breathing.
JOANNE FARYON: The family was aware of the whooping cough epidemic in California from news reports.
T.V. REPORTER: State health officials say more than 6,400 cases of whooping cough have been reported this year.
JOANNE FARYON: Matthew's doctors suspected it could be whooping cough, also known as pertussis. She took a nasal swab and sent it to the lab. She also started Matthew on antibiotics.
Six days later, with Matthew just 23 days old, Cindy Bryce got a phone call from the California Department of Health. The diagnosis was whooping cough.
Pertussis is a respiratory illness caused by the bacterium Bordetella pertussis. At first, it can mimic a cold, but later produces a violent and persistent cough, a cough that leaves children gasping for air creating that distinct whooping sound.
For adults, whooping cough may only be a nuisance. But to infants, whooping cough can be deadly, especially if not diagnosed early.
Whooping cough was nearly wiped out by the late 1970s because of mass immunization, but it somehow found its way back to California and other highly vaccinated communities around the world. Just why it's made such a vengeful comeback has two of the world's leading whooping cough experts in disagreement.
Dr. James Cherry of UCLA.
JAMES CHERRY, UCLA: The main reason is increased awareness.
JOANNE FARYON: And Dr. Frits Mooi of The Netherlands Center for Infectious Diseases Control.
FRITS MOOI, The Netherlands Center For Infectious Diseases Control: We found really a kind of new mutation in the bug.
JOANNE FARYON: The bacterium that causes whooping cough was first isolated in Belgium in 1906. At the time, the illness was one of the leading causes of infant death. The discovery led to the first attempts at a vaccine. But it wasn't until the late 1940s, scientists developed a vaccine effective enough to prevent whooping cough.
T.V. ANNOUNCER: Unlike the disease, however, a vaccine does not endanger life.
JOANNE FARYON: By 1946, mass immunization programs began in the U.S. and the numbers of cases dropped dramatically.
Prior to the vaccine, the rate of disease was 157 cases per 100,000. By the 1970s, with large-scale immunizations, fewer than one in 100,000 people got whooping cough.
But the vaccine was not without controversy. The early versions were associated with side effects such as prolonged crying spells and seizures in babies. By 1996, the FDA approved a new whooping cough vaccine. It was called an acellular version. That means the vaccine uses only purified components of the disease-causing organism.
That vaccine was considered to be safer and associated with few mild side effects. Today, the U.S. uses only the acellular pertussis vaccine.
WOMAN: And then you're getting the Tdap shot which includes the whooping cough.
JOANNE FARYON: But as the United States was changing vaccines, something else was happening.
Health officials across the country were reporting increasing numbers of positive whooping cough cases. And in a government lab, about 30 minutes outside of Amsterdam, a group of scientists had discovered something else. The bacterium that causes whooping cough started to look a little different.
FRITS MOOI: And so this new mutation had the effect that the bacteria started to produce more pertussis toxin.
JOANNE FARYON: Just whether that mutation is to blame, at least in part for the California epidemic and outbreaks elsewhere in the world, is at the heart of the whooping cough debate.
JAMES CHERRY: Even though these changes occurred, they haven't -- there's no evidence that that's led to increased vaccine failure.
JOANNE FARYON: Just how effective is vaccine? That all depends on who you talk to. Drug information included with the two most commonly used whooping cough vaccines in the U.S. say the vaccine is 85 percent effective.
Dr. Mooi believes there's no way to determine how effective the vaccines are because they have not been tested against the new strain of whooping cough.
FRITS MOOI: We call it the P3 strain.
JOANNE FARYON: A strain he believes is more virulent and can make people sicker. The strain emerged while the new acellular vaccines were being developed.
FRITS MOOI: Well, I can tell you one of the reasons why the vaccine companies are not too happy with me is that if what I say is true, they selected the wrong strains in the 1980s.
JAMES CHERRY: There's absolutely no evidence that either of the two vaccines that are most common today in -- in -- used in the U.S., that there's increased vaccine failure with either of those vaccines.
JOANNE FARYON: Cherry says the increase is also due in part because of something called waning immunity. Immunity to whooping cough does not last a lifetime. Whether you're vaccinated or developed natural immunity from getting the disease, almost all experts agree waning immunity is contributing to whooping cough outbreaks worldwide.
Where they disagree, when does immunity fail?
Dr. Mooi says public health officials should be encouraging cocooning, immunizing all those around newborn babies. But in the long run, he says, we need better vaccines.
Baby Matthew spent four days in the hospital and was eventually discharged. Today, he's getting his two-month routine checkup. Despite a stuffy nose, Matthew is doing well.
TERESA HARDISTY: As you might know, the vaccine is not as effective as we want it to be and that's one reason why there have been a lot of cases going around. But with Matthew, in particular, he -- his own immunity has kicked in, you know, from having the elements that is, in effect, sort of a booster, if you will, that will protect him going forward. And how long that immunity lasts, there's still a question mark.
GWEN IFILL: This report was part of a larger series KPBS in San Diego has done on the reemergence of whooping cough. To watch it all, go to our website at newshour.pbs.org and follow the link to the special documentary site at KPBS.